This application is based on application No. JP 2001-177813 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an improved light shutter device. More particularly, the present invention relates to a light shutter device including plural electrodes in an opposite structure provided on a substrate made of a material having an electro-optical effect and light modulation regions each sandwiched between electrodes.
2. Description of the Related Art
Heretofore, there have been used light shutter devices, each having plural light modulation regions provided on a substrate made of PLZT or LiNbO3, which are materials having an electro-optical effect, each including the substrates arranged in array, and on/off controlling light, in an external light modulator for use in large capacity optical communication, an optical path change-over switch in an optical time domain reflectometer or an optical signal generator for an optical printer.
To be detailed, as shown in FIG. 5, a voltage is applied between electrodes 32 and 33 of one pair provided on a PLZT substrate (a light shutter chip) 30 to thereby generate an electric field, to produce a birefringence in PLZT, to convert light incident on a light shutter element (a light modulation region) 31, the light being transmitted through a polarizer 41 installed at the previous stage thereof, to 90 degree polarized light and to finally cause outgoing light to be transmitted through an analyzer 42. On the other hand, in a case where no electric field is generated, light transmitted through the polarizer 41 is transmitted through the light shutter element 31 without being polarized, but intercepted by the analyzer 42.
In such a light shutter element 31, the maximum quantity of transmitted light can be obtained when incident light is converted to 90 degree polarized light, and an applied voltage at this time is called a half wavelength voltage.
In FIG. 6, there is shown an electrode pattern formed on a chip 30 adopted in a prior art light shutter device. On the chip 30, there are formed a common electrode 32 grounded and individual electrodes 33 opposite it and light shutter elements 31 are formed between the electrodes 32 and 33. The individual electrodes 33 are connected to bonding pads 33b through respective lead electrodes 33a, while the common electrode 32 is also connected to bonding pads 32b through respective lead electrodes 32a. 
In a case where this kind of a light shutter device is used in forming an image, a requirement arises for thousands of light shutter elements 31 in exposure across a length of the order of 30 cm in the main scan direction indicated by an arrow mark X. This requirement is difficult to realize with one chip 30 but instead, an array architecture is adopted in which chips 30 on each of which hundreds of elements 31 are formed are juxtaposed in parallel with each other along the arrow mark X direction. Moreover, the light shutter elements 31 are arranged in a double rowed, zigzag pattern and on/off controlled at prescribed timings in each row, thereby forming an image of one line on an exposed surface moving in the sub-scan direction indicated by an arrow mark Y.
Attention being focused on a group of light shutter elements 31a, 31b, 31c and 31d, variations in half wavelength voltage arise among the elements because of differences in position of the elements and shapes of electrodes around an element on a chip. That is, since the elements 31a and 31d are located at an end of a chip 30, electric fields applied by the electrodes 32 and 33 tend to be confined, thereby strongly acting on the elements 31a and 31d as compared with electric fields of other elements 31b and 31c and so on. On the other hand, in comparison between the elements 31b and 31c, an electric field of an element is different according to whether a lead electrode 32a is located on the acute angle side or the obtuse angle side of an individual electrode 33. A lead electrode 32a adjacent to the element 31c is located on the acute angle side of an individual electrode 33; therefore, an electric field applied between the electrodes 32 and 33 leaks into the lead electrode 32a more than in the case of the element 31b located on the obtuse angle side of an individual electrode 33, thereby weakening the electric field in the element 31c as compared with an electric field in the elements 31b. An influence of a lead electrode 32a is equally exerted on the elements 31a and 31b. 
In FIG. 7, there are shown relationships of a quantity of transmitted light versus an applied voltage of the respective light shutter elements 31a, 31b, 31c and 31d. Since each of the elements is driven by a prescribed voltage, variations in half wavelength voltage, as shown in the figure, result in differences in transmitted quantity, leading to variations in light quantity. For example, if a light shutter device is employed in recording of an image, uneven transmitted quantity is observed as unevenness in image density, resulting in degradation of an image quality.
The present invention has been made in light of such circumstances and it is an object of the present invention to provide an improved light shutter device. That is, the object is to provide an improved light shutter including plural electrodes in an opposite structure provided on a substrate made of a material having an electro-optical effect and light modulation regions each sandwiched between electrodes. More particularly, it is an object of the present invention to provide a light shutter device capable of suppressing variations in quantity of transmitted light among light modulation regions regardless of differences in position of a light modulator element and pattern of electrodes around of a light modulator element on a substrate.
In order to achieve the object and other objects, a light shutter in an aspect of the present invention includes: a substrate made of a material having an electro-optical effect; and plural electrodes in an opposite structure provided on the substrate, wherein a region between electrodes of each pair on the substrate becomes a light modulation region and thereby the region serves as a light shutter, and a spacing between and/or a shape of electrodes in an opposite structure is made different according to an environment in which the light modulation region is placed, thereby almost equalizing half wavelength voltages of light modulation regions.
With such a construction adopted, variations in quantity of transmitted light among light modulation regions can be suppressed.
In another aspect, the environment is a position on the substrate of the light modulation region.
In still another aspect, the environment is a pattern of electrodes located around of the light modulation region.
In yet another aspect, the spacing between electrodes of a pair forming a light modulation region is narrower in an environment thereof having an electric field weaker in action, while being wider in an environment thereof having an electric field stronger in action.
In a further aspect, a wider spacing is set between electrodes of a pair forming a light modulation region located at an end of the substrate.
In a still further aspect, that the shape of electrodes is made different means that an areas of an electrode is made different.
In a yet further aspect, an electrode area of an electrode forming a light modulation region located at an end of the substrate is narrowed.
In another aspect, the light modulation regions are arranged zigzagging in 4 rows and a spacing between electrodes of a pair forming a light modulation region in the inner side of the 4 rows is narrower than in the outer side thereof.
A light shutter device instill another aspect includes a shielding layer having a window defining an aperture through which light is transmitted for each light modulation region, and.
In yet another aspect, a window of the shielding layer defines the aperture with a light modulation region formed between electrodes in an opposite structure having the smallest spacing therebetween as a criterion.
With such a construction, for example, in a case where a light shutter device is used in recording an image, sizes of pixels can be made uniform by windows.
Moreover, a light shutter device in a further aspect includes: a substrate made of a material having an electro-optical effect; and plural electrodes in an opposite structure provided on the substrate, wherein a region between electrodes of each pair on the substrate becomes a light modulation region and thereby the region serves as a light shutter, and at least one factor of a spacing between and a shape of electrodes in an opposite structure sandwiching each light modulation region is made different, thereby almost equalizing half wavelength voltages of light modulation regions.